462 DESCBIPTIOK OF .[Polygostrica. 



At the broad anterior end are two notches, looking like openings, and 

 one in the centre of both the dorsal and ventral surface. The stalk 

 is an excreted, immovable, horny substance ; at its attachment to the 

 lorica there is no opening in the latter ; it can detach itself, move 

 about independently, and probably form another stalk. In some in- 

 stances the lorica appears to be transversely striated internally. 



This genus resembles Cocconema, but the finstules of the latter are 

 cymbiform, and not cimeiform. 



This genus gives name to a family Gomphonemece in the system of 

 Kiitzing, which includes, besides, the genera Sphenella and SpJienosira. 



" This genus, Gotnphonetna," says Mr. Kalfs (Ann. Nat. Hist. vol. 

 xii. p. 459, 460) "borders closely on Styllaria and Licmophora, and, 

 as it were, forms a connecting link between them. It is only in a 

 young state that, in a few instances, its frustules are sessile, and 



resemble those of Styllaria, which are always sessile Its 



connexion is still more intimate with Lianophora ; and Mr. Bailey 

 observes, that in Licmophora the jfrustules again divide, which is the 

 sole difference between the two genera." Kiitzing, however, dis- 

 covers two points of distinction besides : 1 . The presence of a clear 

 central opening on the ventral sui'face, which is absent in Licmophora ; 

 and 2. The absence of the longitudinal stiipes, which are seen on the 

 dorsal aspect of Licmophora near each margin. 



"In the wedge-shaped figui'e of its frustules, Gomphonemais,a,?,sam- 

 lated also to detached segments of Meridon or of some Biatoma, but 

 differs fi'om them in having the central aperture; besides which, its 

 transverse striaa do not traverse the surface unbroken (Ralfs loc cit.) 

 The frustules situated at the extremities of the dichotomous 

 branches are generally simple, or binate. I have never seen more 

 than six frustules from the same point, and even when more than 

 two are thus occasionally combined, they arc usually in contact only 

 at the base. In Licmophora, on the contrary, the stipes is iiTcgularly 

 branched, and each branch terminated by several frustules, often ten 

 or more, united by their sides in a fan-like form. Besides these 

 terminal clusters, the main trunks of the stipes have binate or ternate 

 frustules, sessile, or nearly so, along their margins, and either oppo- 

 site or alternate." 



"The notches, like puncta, ia the upper margin, are, in some 



